The present invention relates to a method of sensitively and quickly detecting minute defects in semiconductor substrates or the like and an apparatus for carrying out the method.
A production line for producing semiconductor substrates or thin-film substrates typically includes the inspection of semiconductor substrates or thin-film substrates for foreign that may be adhering to the surfaces of semiconductor substrates or thin-film substrates so as to monitor the dust producing condition of the manufacturing equipment. For example, minute foreign matter of 0.1 μm or below that is adhering to a surface of a semiconductor substrate needs to be detected before forming a circuit pattern on the surface of the semiconductor substrate. Techniques for detecting minute defects on a sample semiconductor substrate, as disclosed in U.S. Pat. Nos. 4,601,576 and 5,798,829, involve the scanning of the entire surface of the sample semiconductor substrate with a laser beam of several tens of micrometers in diameter by turning and translating the sample semiconductor substrate, and light scattered by foreign matter and defects is detected to inspect the surface of the semiconductor substrate for foreign matter and defects.
In a SOI wafer (silicon-on-insulator wafer), a BOX layer (oxide film) and a SOI layer (Si), each having a thickness in the range of several tens of nanometers to several hundreds of nanometers, are formed in layers on a bulk Si. Therefore, the intensity of scattered light that have been scattered by foreign matter and defects varies according to the thickness of the BOX layer and the SOI layer due to the influence of thin-film interference. A method disclosed in JP-A No. 6-102189 uses an illumination angle that makes the intensity of light reflected in a regular reflection mode maximum to avoid the variation of detection sensitivity due to the influence of thin-film interference. This known method, however, can not deal with an intralayer thickness variation. Methods disclosed in JP-A Nos. 2001-281162 and 2003-166947 use light of a plurality of wavelengths for illumination to reduce the influence of thin-film interference.